The present invention relates to an insulation arrangement for reducing machine vibrations and, more particularly, to an engine mount for mounting a naturally aspirated gasoline engine in passenger and commercial motor vehicles as well as motor vehicles equipped with diesel engines having a vacuum pump.
In order to enhance the riding comfort in passenger compartments of, for example, passenger motor vehicles, there have been a number of proposals seeking to provide greater flexibilities for the engine mount with an aim toward filtering out high frequencies. These greater flexibilities may cause a phenomenon known as "chop" or resonance in the suspended masses of the motor vehicle which may occur, for example, on good roads with wavy coating. To counteract this phenomenon, it is necessary to take steps to damp the displacements of the engine mounts wich would excess one millimeter.
Various devices such as, for example, hydraulic arrangements have been proposed which attempt to counteract the above-noted phenomenon without interferring with the filtering effect of the high frequency vibrations, with a nearly universal solution for a power unit or engine mount taking the form of a rubber support structure.
More particularly, in order to allow for a flexibility of several millimeters under load, it has been proposed to utilize one or more circular conical sections provided with a thick rubber shell, working both in shear and in compression which makes it possible to form a variable volume enclosure defining two chambers between which a liquid such as, for example, a hydraulic fluid, is transferred so as to enable an absorption of the high frequency oscillations.
One disadvantage of the above proposed hydraulic mounts resides in the fact that, by virtue of the realiance of the mounts on a damping fluid, there is a chance not only of a leakage of the damping fluid but also, in certain circumstances, a freezing of the damping fluid thereby adversely affecting the overall performance of the mount, reducing the life span thereof, and increasing the overall maintenance requirements.
Yet another disadvantage of the above noted proposed hydraulic mounts resides in the fact that, aside from being relatively complicated, the mounts also have a substantial weight thereby increasing the total weight of the vehicle suspension system.
The aim underlying the present invention essentially resides in providing an insulation arrangement such as, for example, a vibration damping engine mount for passenger or commercial motor vehicles which avoids, by simple means, the above-noted shortcomings and disadvantages encountered in the prior art.
In accordance with advantageous features of the present invention, a damping arrangement such as, for example, pneumatic engine mount for a passenger or commercial motor vehicle is provided which includes a membrane forming an enclosure or chamber of a variable volume, with the membrane being fashioned of a thick rubber wall bonded to reinforcement members. The damping arrangement is constructed so as to bear a force or load greater than the suspended load and, in fact, the force sustained is even greater due to the fact that, in accordance with the present invention, a moderated vacuum is provided which creates a static balance lower than the static position of the loaded membrane forming the chamber or enclosure. The vacuum that exists inside the chamber is modulated by a rapid connection of the enclosure to one of two additional chambers or enclosures on either side thereof with a slight clearance around a balance position of the load. On one hand, to allow the increase of the load, a limited volume previously brought to atmospheric pressure through a filter with a small opening section or, on the other hand, to allow a decrease of the load, another limited volume, previously subjected to a maximum vacuum of an engine or a vacuum pump, makes it possible to create an accelerating force to correct a displacement of the load when one of the two rapid connections is open. By virtue of these features, the accelerating force is limited to an acceptable value for comfort in a passenger compartment of the passenger or commercial vehicle of, for example, 0.2 times the value of the weight of the engine unit of the vehicle.
In order to compensate for a tendency of an oscillating cycle of notable amplitude to occur, a progressive return to atmospheric pressure on the one hand, and a maximum vacuum, in each of the chambers or enclosures provides a positive action that opposes the displacement of the load thereby providing active absorption of the displacement which can easily exceed a disturbing force at the origin of the displacement.
Advantageously, in accordance with further features of the present invention, the enclosure or chamber of variable volume is formed by two conical spring members or encasements formed of, for example, rubber, with the conical spring members being arranged so that the respective flexibilities thereof are disposed in a series in order to enable a bearing of the weight of a suspended load.
In order to enable a rapid connection of the variable volume chamber or enclosure, connection valve means are interposed between the additional chambers or enclosures and the variable volume chamber or enclosure.
The two additional chambers or enclosures, in accordance with the present invention, may have a common encasement with a rigid armature of the enclosure whose shape can be altered and superimposed on the rubber engine mount. Moreover, the atmospheric pressure return valve may be produced from a material that can change its shape such as, for example, a cellular elastomer, with a small amount of leakage being distributed throughout the encasement.
Other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which show, for the purposes of illustration only, one embodiment in accordance with the present invention .